Sound Reinforcement Flashcards
What is the speed of sound?
1130ft./second (at sea level and temp 59 degrees F
What is the overall frequency band of the human voice?
100Hz - 6kHz
Outdoor audio systems face three things to overcome. What are they and what is the effect of each?
Wind (velocity, gradient)
Temp (speed)
Humidity (attenuation)
Each time you double the number of open microphones, the system gain must be what to avoid feedback?
System gain must be reduced by 3dB to avoid feedback per microphone
What is the difference between a condenser microphone and a dynamic microphone?
Condensers use amplifiers; used in recording.
Dynamic - stage use, like a miniature loudspeaker.
What can cause “hum” noise in a sound system?
Bad power supply / AC leakage.
A loudspeaker’s sensitivity rating denotes what?
Efficiency rating of the driver
What converts electrical energy into acoustic energy?
Output transducers
What converts acoustic energy into electrical energy?
Input transducers
Define dynamic range
The difference (in decibels) between the loudest and the quietest portion of the program.
What is special about a lavalier microphone?
Doesn’t have proximity effect; attached to the person so sound quality is more consistent.
A passive crossover is sensitive to two things. What are they?
Source impedance (driving), and load impedance
What audio component can directly drive a loudspeaker?
No answer provided on sheet
Define what each of the following does: Multi-band equalizer - High pass filter - Low pass filter - Compressor - Limiter - Noise Gate -
Multi-band equalizer - allows the frequencies of each band to be adjusted.
High pass filter - (low cut filter) allows all frequencies above its cutoff point to pass through from filter input to filter output without attenuation.
Low pass filter - (high cut filter) attenuates frequencies above a certain cutoff point
Compressor - ratio of change from input level to an output level.
Limiter - allows signals below a specified input power or level to pass unaffected while attenuating (lowering) the peaks of stronger signals that exceed this threshold
Noise Gate - used to control the volume of an audio signal; attenuates signals that register below the threshold.
Define what each of the following does: Multi-band equalizer - High pass filter - Low pass filter - Compressor - Limiter - Noise Gate -
Multi-band equalizer - allows the frequencies of each band to be adjusted.
High pass filter - (low cut filter) allows all frequencies above its cutoff point to pass through from filter input to filter output without attenuation.
Low pass filter - (high cut filter) attenuates frequencies above a certain cutoff point
Compressor - ratio of change from input level to an output level.
Limiter - allows signals below a specified input power or level to pass unaffected while attenuating (lowering) the peaks of stronger signals that exceed this threshold
Noise Gate - used to control the volume of an audio signal; attenuates signals that register below the threshold.
What are the three functional groups of an audio system?
input transducers, signal processing, and output tranducers
Define compression ratio, as applied to audio systems.
An audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds thus reducing or compressing an audio signal’s dynamic range. The amount of gain reduction is determined by ratio: a ratio of 4:1 means that if input level is 4 dB over the threshold, the output signal level is 1 dB over the threshold. The gain (level) has been reduced by 3 dB:
Threshold = −10 dB Input = −6 dB (4 dB above the threshold) Output = −9 dB (1 dB above the threshold)
What is the typical impedance of a balanced, low-impedance line input?
600 Ω
What types of cables should typically be kept to 10 feet or less in length?
unbalanced cables
What is the common name for a pin connector and who invented it?
RCA
What is/are the primary cause(s) of noise in a sound system?
ground loop, grounding
What are the best connections for rejecting ground loops and other electrical noise?
differential connections
What piece of test equipment would you use in the following situations:
a. You need to test the polarity of a circuit.
b. You need a known signal source.
c. You have a pink noise generator as your test signal source.
d. When you want to record the physical waveform display.
e. You need to measure loudness.
a. You need to test the polarity of a circuit
b. You need a known signal source.
c. You have a pink noise generator as your test signal source.
d. When you want to record the physical waveform display.
e. You need to measure loudness.’‘The following items are used for basic measurement of voltages, currents, and components in the circuit under test.
Voltmeter (Measures voltage)
Ohmmeter (Measures resistance)
Ammeter, e.g. Galvanometer or Milliameter (Measures current)
Multimeter e.g., VOM (Volt-Ohm-Milliammeter) or DMM (Digital Multimeter) (Measures all of the above)
LCR meter - inductance (L), capacitance (C) and resistance (R) meter (measure LCR values)
The following are used for stimulus of the circuit under test: Power supplies Signal generator Digital pattern generator Pulse generator Howard piA digital multimeter
The following analyze the response of the circuit under test: Oscilloscope (Displays voltage as it changes over time) Frequency counter (Measures frequency)
Any piece of equipment used for sound reinforcement should cover what frequency range?
No answer provided on sheet
What is the best shielding you can use in a permanent install, or within a rack or piece of equipment?
Foil - it’s cheaper and lightweight. Braided is more versatile for moving around
What is the function of a mixer?
An audio mixer takes two or more audio signals, merges them together and provides one or more output signals.
With respect to cabling, magnetic fields are only canceled by two things. What are they?
physical distance and twisting
